1. Field of the Invention
The invention relates to a method which, with the aid of complex-forming agents, enables the production of alkyloligoglycosides and alkylglycosides having alkyl groups with 8 to 24 carbon atoms.
2. Discussion of the Background
Alkyloligoglycosides and alkylglycosides with alkyl groups having 8 to 24 carbon atoms can be prepared partially or completely from many types of raw materials. These alkyloligoglycosides and alkylglycosides are becoming increasingly important, due to their interesting surface-active properties combined with very good biodegradability. For use in the home economics and cosmetics sectors, these products must meet stringent esthetic requirements. Therefore methods are sought by which alkyloligoglycosides and alkylglycosides can be produced in aqueous solutions, and which are transparent and have an attractive color.
In the production of alkyloligoglycosides and alkylglycosides with long-chain alkyl groups, one generally first employs glycosidation of saccharides with short-chain alcohols, to produce alkyloligoglycosides and alkylglycosides with alkyl groups having 1 to 6 carbon atoms. These intermediate products are then converted to the desired alkyloligoglycosides and alkylglycosides by transglycosidation, at elevated temperature. However, the products thus produced are dark in color.
According to European Pat. No. 165,721, the color of such products can be improved by multistage bleaching with hydrogen peroxide, and can be stabilized by addition of compounds which liberate sulfur dioxide. The lightening effect is only of short duration in the absence of sulfur dioxide.
According to European Pat. No. 77,167, reducing agents such as hypophosphorous acid or sulfurous acid can be added in the reaction of alcohols with aldoses or ketoses. The color of the alkylglycosides is thereby improved. Small amounts of reducing agents are effective with this method only if the process is carried out with the exclusion of oxygen.
Preventive measures are also known. Thus, according to European Pat. No. 102,558, one obtains C.sub.3 to C.sub.5 alkylglucosides of improved color if the glucosidation is carried out in the presence of an alkali salt of a boron acid.
In preparing long-chain alkylsaccharides, according to U.S. Pat. No. 4,465,828, color improvement can be obtained with the aid of the hydroxypolycarboxylic acids such as citric acid, tartaric acid, and malic acid. However, the improvement achieved in light-permeability of the solutions is inadequate for many applications.
According to U.S. Pat. No. 4,483,979, coloring factors can be extracted from alkylpolysaccharides. This costly procedure requires anhydrous polar solvents. In addition, part of the alkylpolysaccharides are extracted in the process, along with the colorants.
According to European Pat. No. 99,183, water-containing polysaccharides can be reacted with alcohols to form light-colored alkylglycoside solutions. However, the method requires cosolvents such as methanol and acetone, and leads to reaction mixtures with a high content of unconverted saccharide.
European Pat. No. 132,064 discloses that alkylglycoside solutions can be neutralized, after completion of the reaction, by means of alkali alcoholates or alkali salts of carboxylic acids. In this connection, sodium methoxide leads to only a slightly more than 50% reduction in absorption in the visible range, in comparison to sodium hydroxide.
The known methods of producing alkyloligoglycosides of improved color are cumbersome, require expensive reagents, or else do not lead to the desired color qualities.